Ophthalmic prescriptions for eyeglass lenses use a standardized nomenclature to identify the combination of lens characteristics that are needed to correct a particular person's vision. Dispensing opticians do not stock prefabricated lenses of all possible combinations that may be needed as this would require an impractically large inventory. Thus the lenses that are specified in most prescriptions must be individually fabricated at the time that the prescription is filled.
Filling a prescription by the traditional process of grinding and polishing lens blanks is undesirably costly and time consuming. The process is particularly complicated if the prescription calls for multi-vision lenses such as bifocals or trifocals.
Fabrication of lenses by laminating lens wafers together with a light transmissive adhesive is a simpler and faster procedure for filling individual prescriptions. The optician maintains a stock of lens wafers of incrementally differing optical properties and selects a front and a back wafer which meet the lens requirements of a particular prescription when the wafers are laminated together. A limited number of back wafers of incrementally different sphere powers, for example, can be paired in different combinations with ones of a smaller number of front wafers of differing base curves to produce lenses having a large number of different through sphere powers. This makes it possible to fill most prescriptions with a wafer inventory of practical size.
In addition to a spherical correction for nearsightedness or farsightedness, a prescription may call for any of various degrees of cylinder correction for astigmatism and in the case of multi-vision lenses also specifies a degree of add power and a segment style configuration for the bifocal, trifocal or progressive insert. Thus the stocked wafers include a number of wafers of each sphere power or base curve that differ from each other in these other respects.
In the prior practice of this method of lens lamination, each wafer is individually packaged and the back wafer packages display the sphere power of the wafer itself while the front packages display the base curve of the wafer which is the nominal curvature of the convex front surface of the front wafer. This data does not enable a direct selection of the particular front wafer and back wafer that are needed to provide a lens with the sphere power called for in a prescription. The optical technician must consult a component selection chart or table which identifies the particular wafers that are needed to provide the prescribed spherical correction.
Lens fabrication could be effected more quickly and efficiently and with less risk of error if reference to a selection chart or table was unnecessary.
The prior procedure does not provide any convenient procedure for cross checking or verifying, prior to lamination, that the correct pair of wafers have in fact been obtained from stock other than by again referring to the selection chart or table. It would be advantageous and less subject to mistake if this could be accomplished in a simpler, less time consuming manner.
The present invention is directed to overcoming one or more of the problems set forth above.